Ash Deposition during Oxy-coal Combustion under High Inlet O_2 Concentration Conditions

摘要

Oxy-coal combustion has been considered a promising technology for CO_2 capture for coal fired power plant. Ash deposition plays a significant role among the issues that determine the design and operation of coal utilization equipments, so a comprehensive understanding of ash deposition characteristics is essential in oxy-coal combustion technology. Previous studies on ash deposition normally treat the deposits as a bulk, inevitably ignoring lots of details. In this work, a temperature controlled deposits sampling probe was applied for deposit ash sampling in 50% O_2 inlet oxy-coal combustion with once through CO_2 as well as air combustion on OFC. Deposits from different position of the sampling probe (60°-120°, vertical, horizontal) were investigated. As initial layer deposits played an important role in ash deposition, horizontal deposits was separated into inside and outside deposits, where inside deposits was an approximation of initial layer deposits. In addition, the effect of the sampling parameters (probe surface temperature, sampling port flue gas temperature and sampling holding time) on deposits formation was also investigated. The results showed that (1) deposits from different position of the probe exhibited difference in both compositions and particle size distribution; (2) no significant effect of holding time on compositions of both inside and outside deposits was found, but their particle size was increasing with time; (3) lower sampling probe surface temperature enhanced the vertical deposition rate; (4) lower flue gas temperature led smaller Weber number which resulted in larger possibility to capture big particles; (5) no significant difference was found in compositions of outside deposits from OXY50 and air, however, inside deposits from OXY50 had higher Si and Fe while lower S and Na comparing to that of air combustion, which might be caused by the big Fe-silicate glass, and this was supposed to differ the properties of the initial layer deposits of OXY50 from that of air combustion.